a(0)=1, a(1)=2, a(2)=1; for n>2, a(n) = 7*2^(n-3)-2.

Terms

a(0) =1a(1) =2a(2) =1a(3) =5a(4) =12a(5) =26a(6) =54a(7) =110a(8) =222a(9) =446a(10) =894a(11) =1790a(12) =3582a(13) =7166a(14) =14334a(15) =28670a(16) =57342a(17) =114686a(18) =229374a(19) =458750a(20) =917502a(21) =1835006a(22) =3670014a(23) =7340030a(24) =14680062a(25) =29360126a(26) =58720254a(27) =117440510a(28) =234881022a(29) =469762046